A new class of cytoplasmic mutants (mit negative mutants) of yeast will be studied biochemically and genetically. The mutants have specific lesions in enzymes of the mitochondrial inner membrane that contain subunit proteins translated on mitochondrial ribosomes. The objectives of the genetic studies will be to localize and map the mit negative mutations on the mitochondrial circular DNA. This will be done by several methods, including crosses of the mutants to a large number of rho negative testers, by recombination mapping and three point crosses, and by heteroduplex mapping using restriction fragments of mitochondrial DNA. The objectives of the biochemical studies will be to establish which of the mit negative loci code for structural and/or regulatory genes. In addition the mutants will be used to probe the function of the defective subunits in the function of parent enzymes and in the mechanism of assembly of the enzymes.